Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$35.48	6.590%	$37.8181	$37.82	$37.80	$37.80
Purchase #2	$197.28	7.134%	$211.354	$211.35	$211.35	$211.40
Purchase #3	$121.86	9.849%	$133.862	$133.86	$133.85	$133.90
Purchase #4	$210.83	5.331%	$222.0693	$222.07	$222.05	$222.10
Purchase #5	$185.32	9.596%	$203.1033	$203.10	$203.10	$203.10
Purchase #6	$18.59	12.153%	$20.8492	$20.85	$20.85	$20.80
Purchase #7	$250.90	4.515%	$262.2281	$262.23	$262.25	$262.20
7 purchase totals =	$1,020.26		$1,091.2840	$1,091.28	$1,091.25	$1,091.30